But Dave Allan doesn't worry much about
Zeno. To Allan a second is virtually infinite.
"We can split a second into as many pieces as
our technology allows. There appears to be no
limit. Timekeeping is our own invention."
The clock instructs us when-maybe even
how - to behave. Each hour is a little bucket of
time to fill. The clock says when to pour.
Nature too has its clocks. We can read them
almost everywhere if we have the tools. In
1947 American chemist Willard Libby found a
clock ticking in virtually everything that lived
during the past 50,000 years-the carbon-14
atom, which decays at a known rate. By com
paring carbon-14 atoms with atoms that don't
decay, scientists can tell the age of a pharaonic
mummy or an ancient Indian hearth.
Using similar techniques, geologists can
measure decay rates of radioactive elements
like uranium, potassium, or rubidium to set
ages for the planet's many tiers of rock. Those
at the floor of the Grand Canyon reveal two
billion years of geologic history, while rocks in
northwest Canada go back nearly four. Moon
rocks date back 4.5 billion years, about the
same age estimated for the earth.
Astronomers have gazed even further back
in time. By looking at light from a faraway gal
axy, they are actually looking at the galaxy as it
was billions of years ago -today the best way
to travel in time. The rate at which these galax
ies are flying away from each other tells them
the date when all the matter in the universe set
out on its journey.
"We were able to show that the matter in
the universe must have been infinitely com
pressed and dense about 15 billion years ago,"
says theoretical physicist Stephen Hawking of
England's Cambridge University.
And before that? "Time as we measure it
"0 for an engine to keep back all clocks." English poet Ben Jonson gave voice in
the 17th century to our ageless lament over the brevity of human life. It echoes in
a woman's grieffor her younger sister, a budding writer and musician, who at
34 lies near death in a Cleveland hospital following surgery to remove a tumor.
National Geographic, March 1990
126